From cd823db8b1161ef0d756514d280715a576d65cc3 Mon Sep 17 00:00:00 2001 From: Petri Gynther Date: Wed, 29 Jun 2011 11:36:11 +0200 Subject: [PATCH] i2c/pca954x: Initialize the mux to disconnected state pca954x power-on default is channel 0 connected. If multiple pca954x muxes are connected to the same physical I2C bus, the parent bus will see channel 0 devices behind both muxes by default. This is bad. Scenario: -- pca954x @ 0x70 -- ch 0 (I2C-bus-101) -- EEPROM @ 0x50 | I2C-bus-1 --- | -- pca954x @ 0x71 -- ch 0 (I2C-bus-111) -- EEPROM @ 0x50 1. Load I2C bus driver: creates I2C-bus-1 2. Load pca954x driver: creates virtual I2C-bus-101 and I2C-bus-111 3. Load eeprom driver 4. Try to read EEPROM @ 0x50 on I2C-bus-101. The transaction will also bleed onto I2C-bus-111 because pca954x @ 0x71 channel 0 is connected by default. Fix: Initialize pca954x to disconnected state in pca954x_probe() Signed-off-by: Petri Gynther Signed-off-by: Jean Delvare Cc: stable@kernel.org --- drivers/i2c/muxes/pca954x.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/drivers/i2c/muxes/pca954x.c b/drivers/i2c/muxes/pca954x.c index 54e1ce73534b..6f8953664636 100644 --- a/drivers/i2c/muxes/pca954x.c +++ b/drivers/i2c/muxes/pca954x.c @@ -201,10 +201,11 @@ static int pca954x_probe(struct i2c_client *client, i2c_set_clientdata(client, data); - /* Read the mux register at addr to verify - * that the mux is in fact present. + /* Write the mux register at addr to verify + * that the mux is in fact present. This also + * initializes the mux to disconnected state. */ - if (i2c_smbus_read_byte(client) < 0) { + if (i2c_smbus_write_byte(client, 0) < 0) { dev_warn(&client->dev, "probe failed\n"); goto exit_free; } -- 2.30.2